SEATTLE (Reuters) – NASA has warned SpaceX and Boeing Co of design and safety concerns for their competing astronaut launch systems, according to industry sources and a new government report, threatening the U.S. bid to revive its human spaceflight program later this year.

NASA is paying SpaceX $2.6 billion and Boeing $4.2 billion to build rocket and capsule launch systems to return astronauts to the International Space Station from U.S. soil for the first time since America’s Space Shuttle program went dark in 2011.

Just ahead of the first scheduled un-manned test flight slated for March 2 under NASA’s multibillion-dollar Commercial Crew Program, NASA’s safety advisory panel cited four “key risk items” in its 2018 annual report earlier this month.

For Boeing, they include the capsule’s structural vulnerability when the heat shield is deployed. For SpaceX, the report mentioned the redesign of a SpaceX rocket canister following a 2016 explosion and its “load and go” process of fueling the rocket with the crew already inside the capsule. “Parachute performance” remained an issue for both companies.

“There are serious challenges to the current launch schedules for both SpaceX and Boeing,” the report said.

Two people with direct knowledge of the program told Reuters that the space agency’s concerns go beyond the four items listed, and include a risk ledger that as of early February contained 30 to 35 lingering technical concerns each for SpaceX and Boeing. Reuters could not verify what all of the nearly three dozen items are. But the sources familiar with the matter said the companies must address “most” of those concerns before flying astronauts and, eventually, tourists to space.

The NASA risk database is updated routinely during the course of NASA’s stringent certification process, which includes data collection, tests and collaboration with SpaceX and Boeing, the people said. The Boeing and SpaceX systems have already been delayed several times in recent years, which is common in this sector given the complexity of building multibillion-dollar spacecraft capable of shedding earth’s gravity.

Reuters